Lead structures for semiconductor components are composed of a lead material and have external leads for external connections and internal leads for electrical connections within a plastic housing composition. Moreover, the lead structures have a chip mounting island composed of the lead material. In the case of surface-mounted semiconductor components, the lead structure comprises similar elements, but only surfaces of leads project from the plastic housing composition as external leads, while the internal areas which are surrounded by plastic housing composition are referred to as internal leads. In both cases, lead structures are involved since they arise with the aid of a leadframe from which the semiconductor components are stamped after completion.
One problem of these lead structures is that the surfaces of the internal leads have to enter into an intensive bonding with the plastic housing composition in order that the internal leads do not break out from the plastic housing composition. A further problem, which occurs at the chip mounting island, is that the top side of the chip mounting island has to be connected to a semiconductor chip, which is usually achieved by means of a conductive adhesive composition. In this case there is the risk of voids forming below the semiconductor chip in the adhesive composition, and of moisture reservoirs accumulating, which can lead to a delamination of the semiconductor chip from the chip mounting island by delamination of the boundary layer either between top side of the chip mounting island and adhesive layer or between adhesive layer and rear side of the semiconductor chip.
In order to improve lead structures of this type, the leadframe, in particular the chip mounting island and the top side of the internal leads, has hitherto been treated by a special deposition of rough coatings with the aid of a special plating or by roughening of the corresponding surfaces of the lead structure or by physicochemical methods, such as plasma etching, such that an intermeshing of the interfaces is achieved.
Even electrolytic coating with adhesion-improving layers based on inorganic and organometallic compounds does not exhibit the desired results. Likewise, the previous adhesion-improving measures such as plasma etching or deposition of inorganic or metallic compounds are extremely expensive and do not yield any significant improvement in the molding composition adhesion and the adhesion of the semiconductor chips on the chip mounting areas of the lead structure.